This invention relates generally to locking devices and, more particularly, to an anti-pick enclosure for a lock having a key slot.
The widely used cylinder lock has several variations of mechanisms that respond to a key in a rotatable portion called a plug within the cylindrical housing.
Of these variations--the pin tumbler and variations of this principle are the most secure locks generally. But another large class of cylinder locks use discs in place of pins.
Nevertheless both general types can be readily compromised with picking techniques, and even the complex improvements of these locks have been opened with special techniques and key substitutes.
Tubular forms of the pin tumbler lock are not significantly superior to the standard type, and are pickable by special tools whose sale from locksmith supply companies cannot be, and are not, successfully limited to authorized locksmiths. Flat key picking devices are similarly not restricted.
Altogether the techniques for picking locks have been well known for some time, and even expensive locks designed to be pick-proof are not. The locks in common use and improvements on these now on the market are not truly secure because the means of picking these locks is still existant. Namely, access to the keyhole and the interior of the lock and its mechanism from outside the lock with minimal interferance to movement and penetration.
The prior art contains examples of various ways of obscuring, covering, and interferring with this free access to the keyway. Examples are French U.S. Pat. No. 3,714,804; Wiczer U.S. Pat. No. 3,765,199 and Adams U.S. Pat. No. 3,267,707. Additionally, Krakauer covers the keyway in U.S. Pat. No. 3,680,337.
Without exception, these examples and all prior art I've been able to discover in this area, either alters the standard key shape, alters the standard pin tumbler lock used as a basis for the improvement, (incidently, the pin tumbler lock as used to the exclusion of other cylinder types of locks entirely) or leaves a restricted but penetratable key slot through which special picking means can be effectively inserted and manipulated.
When a key shape is altered, the user is inconvenienced and charged more for duplicate keys. Keys must be ordered from the factory for replacement or duplication, with the attendant delay and added expense.
When a standard lock is altered, this adds tooling costs to the price of the lock during its amortization period. Depending on the extent of the alteration, it is less competitive in the mass market as a result of such special design requirements.
When any access is left to the lock mechanism internally, it compromises the security of the lock. Such access may slow the process of picking and make it more difficult, but does not prevent it altogether.
All the examples I've been able to locate in prior art make use of a lock with a particularly small range of rotational movement of the plug. As mentioned earlier, this is the pin tumbler type. Tolerances are very small between pins and bores in which the pins operate, so that small amounts of wear on the obscuring means, or covering means, that prevent rotation of the plug until the enclosed mode is attained, over the lifetime of use of the lock, can lead to pressure contact between pins and bores, even when torque is applied in the open protected mode.
This contact becomes the means by which the lock is picked, since the pins can be held in place as they are experimentally lifted to the shear line between the outside of the plug, and the inside of the bore in the cylinder or housing that receives the plug.
In this procedure, the pins are experimentally manipulated to the shear line individually, held there by the pressure possible to exert on them from one side of the bore in the plug, and the opposite side of the bore, holding the same pin, in the cylinder.
When thus arranged and held in positions at the shear line, the closure, whatever its nature, can be moved to the position where it releases the plug to rotate, and as long as some means of exerting a slight torque on the plug is possible, a special key substitute with a spring urging it to rotate is one possibility, the lock can be opened, even within an enclosure.
An object of the present invention is to produce torque on the plug in a cylinder lock in the opposite direction to key rotation, so that pins cannot be held in position at the shear line when individually lifted to the shear line experimentally, without being released as the plug is rotated in the direction that opens the lock. This nullifies the effect that wearing parts that occur during use of the lock, over a period of time, have on the security of such a lock.
A further object is to make use of a standard key that can be duplicated conveniently and economically at hardware stores annd locksmith shops, etc.
A further object of my invention is to make use of a standard pin tumbler, or disc lock, but not limited to these types, in an assembly that will make it invulnerable to picking, without altering the lock if that is desirable. Avoiding alteration of the lock is optional, of course.
A further object of my invention is to prevent drilling out of the lock, when it is used in one optional application, that of a padlock or u-bolt type lock, now being widely used. When used in this application it is placed between the shackle ends, shortening the body or housing of the lock, and requiring any drill bit to enter the soft parts of the lock, housed in a hardened case, at such an angle that the critical securing means behind the standard lock cannot be reached to destroy them, to release the lock.
Another object of my invention is to make the operation of an enclosed lock require a minimum of effort on the part of the user. All the patents cited previously as examples of partially or wholly enclosed key ways protecting locks related and attached to these provisions, require a motion to obscure the keyway, and a second or third motion to operate the lock and made the key accessible for removal again. As an additional convenience, my locking system can be locked without the use of a key by simply pushing against the face of the lock containing the key way, thus moving the lock into its locking mode.
For convenience it is desirable that the user of the lock can elect to keep the lock's key attached, to means of carrying that key. A key chain, ring, or other device can remain attached to the key which is fully enclosed during operation of the lock, without compromising its security.
A small slot in the edge of the enclosure allows no access for picks, but provides this added advantage over other locks that fully enclose the key, or parts of the key.
Other objects are invulnerability to forceful opening, compactness, and protection of the locks mechanism against the enviroment.
Placing the cylinder lock in a position in the housing between the shackle ends, rather than in an extension outside of one end, has other advantages.
Used as a lock for securing two-wheeled vehicles, its short housing makes it more compact for carrying.
It is less subject, in its most common application, that of fastening a vehicle to a fixed object; to damage from blows by a tool.
All other u-bolt type locks of this configuration have an extension holding the cylinder lock beyond one shackle insertion position in the housing.
This extension is commonly from 11/2" to 2" long, and since the center of the housing lies next to the vehicle, or fixed object, and cannot be struck direct blows, the protruding end becomes the vulnerable area to apply effective force. The ends of the housing in my embodiment that lie outside the shackle insertions are minimal, and allow only ineffective glancing blows to be struck at them.
That this means of attacking a u-bolt type lock is acknowledged, is demonstrated by U.S. Pat. No. 4,085,600, granted to Bindari, in which the inventor places an offset in one shackle end, specifically to overhang and protect the extended part of the lock housing from direct blows. This design has found its way into at least two makes of u-bolt locks, now on the market.
Cylinder locks are sometimes forcefully pulled from their locations in a housing by turning a hardened sheet metal screw through the keyslot into the soft brass or diecast parts of the locks mechanism. Then a pounding force is produced by a weight sliding on a rod attached to the screw and having a stop at the other end of the rod.
As the weight is moved rapidly to the end of the slide rod, the stop transfers the kinetic energy in the weight to the rod, which pulls aginst the sheet metal screw. This produces considerable force to dislodge the lock from its seat.
The tool that is applied to this effort is a common one used in auto body and fender work to pull out dents in sheet metal; so it is readily available. The tool cannot be applied as effectively, if at all, when the cylinder lock does not have easy access for forcing the screw into the lock, nor a straight line path for withdrawing it.
Lastly, the enclosure of the cylinder lock, and especially its keyhole during use, protects it against water (from rain and snow) and grit, in the form of airborn particles.
Some padlocks achieve this advantage with the use of a separate enclosing protective plastic jacket with a hinged access port to the keyhole. Others incorporate a keyhole cover in the lock body itself.
The fact, that despite added cost, these features are popular attests to the desirability of protecting the lock mechanism against contaminents.